I ran a test run for speed test of my page. It said "Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network.".
My Page using Play Framework. Came across a lot of answers regarding .htaccess file but it is not supported in Play Framework. How to cache the static files on browser level?
When using Play in production mode, it already sets the ETag header, so whenever a browser requests a file matching that eTag, play just returns 304 Not Modified. This will save you data (the browser will not download the file again if it has the right version), but still requires a request to the server.
If you want to specify a expiracy date, you can use assets.defaultCache="max-age=3600" to your application.conf (adapt the value for your needs: 3600 is one hour in seconds).
I can't check this right now, but I think Play also sets Cache-Control: max-age=3600, so probably the warning you are getting is because this value is too low for the tool you are using to check the caching.
You can also set the expiracy time to individual assets (see https://www.playframework.com/documentation/2.5.x/AssetsOverview#Additional-Cache-Control-directive)
Note that you should only specify a high expiracy time to assets that you are sure that don't change a lot...
Related
I am using webpack to bundle all my assets files so I get something like this.
bundle.7fb44c37b0db67437e35.js
vendor.495e9142a1f8334dcc8c.js
styles.bc5b7548c97362b683f5582818914909.css
I use chunkhash in the name so when browser caches something it doesnt cache again until hash has changed. For example if I change something in styles, bundle the files and deploy, only the hash from styles will change, others wont so browser will request from the server again just the styles file and the rest will use from memory cache.
In response header I also have Etag and Last-Modified and they change every time I deploy app for every file. Should I remove them from response? Can that confuse the browser to contact the server and see if files have changed even though hash is still the same?
Great question. This depends largely on how the back-end is implemented and how it calculates the header values. Are the files served from our server, or something else like s3? Are we using a CDN? Are we using a framework for our application server? Who calculates these headers, the web server or the application server?
For the purposes of this answer and to keep things simple let's assume we are using the popular server framework Express with no CDN or 3rd party hosting. Like most application servers, Express calculates ETag and Last-Modified based on the content of the file being served - not the name of the file.
The first time a browser requests one of our files, it will receive the the ETag and Last-Modified for the resource. The next time the same resource is requested the browser will send the cached ETag and Last-Modified headers to the server. The server then decides based on these headers whether the browser needs to download a new version of the resource or if the cached version is current. If the cached resource is current, the server responds with a 304 - Not Modified status code. The status code is the key to this whole caching system - it is how the browser decides if it should use the cached resource.
To generate the ETag header, Express passes a binary Buffer representation of the response body to the etag module which calculates a SHA-1 hash based on the contents of the Buffer (source: generating ETag header and source: generating hash). To generate the Last-Modified header, Express uses the file system's last modified time (see lastModified in docs).
When webpack builds a new bundle the file's binary will change even if the chunkhash is the same. This causes Express to output a different Etag and Last-Modified, which means it will not respond with a 304 the next time the resource is requested. Without the 304 status code, the browser will unnecessarily re-download the bundle.
Answer
I think the best thing to do here is disable ETag and Last-Modified headers for these assets and instead use the Expires or Cache-Control: max-age header set to a date far in the future (usually 1 year). This way the browser will only re-download a bundle if it is expired or if it simply does not exist in the cache.
As some of you may already know, there are some caching issues in Firefox/Chrome for requests that are initiated by XmlHttpRequest object. These issues mean that browser does not strictly follow the rules and does not go to server for the new XSLT file (for example). Response does not have Expires header (for performance reasons we can't use it).
Firefox has additional parameter in the XHR object "channel" to which you put value Components.interfaces.nsIRequest.LOAD_BYPASS_CACHE to go to server explicitly.
Does something like that exist for Chrome?
Let me immediatelly stop everyone who would recommend adding timestamp as a value of GET parameter or random integer - I don't want server to get different URL requests. I want it to get the original URL. Reason is that I want to protect server from getting too many different requests for simple static files and sending too much data to clients when it is not needed.
If you hit static file with generated GET parameter (like '?forcenew=12314') would render 200 response each first time and 304 for every following request for that value of random integer. I want to make requests that will always return 304 if the target static file is identical to client version. This is BTW how web browsers should work out-of-the-box but XHR objects tend to not go to server at all to ask is file changed or not.
In my main project at work I had the same exact problem. My solution was not to append random strings or timestamps to GET requests, but to append a specific string to GET requests.
If you have a revision number e.g. subversion revision or likewise from git/mer or whatever you are using, append that. Static files will get 304 responses until the moment a new revision is released. When the new release happens a single 200 response is granted and it is back to happily generating 304 responses. :-)
This has the added bonus of being browser independent.
Should you be unlucky and not have a revision number, then make one up and increment it each time you make a release.
You should look into Etags, etags are keys that can be generated from the contents of the file therefore once the file on the server changes the system will be a new etag. Obviously this will be a service-side change which is something that you will need to do given that you want a 200 and then subsequent 304's. Chrome and FF should respect these etags so you shouldn't need to do any crazy client-side hacks.
Chrome now supports Cache-Control: max-age=0 request HTTP header. You can set it after you open an XMLHttpRequest instance:
xhr.setRequestHeader( "Cache-Control", "max-age=0" );
This will instruct Chrome to not use cached response without revalidation.
For more information check The State of Browser Caching, Revisited by Mark Nottingham and RFC 7234 Hypertext Transfer Protocol (HTTP/1.1): Caching.
I implemented RestSharp succesfully in my WP7 application, but one issue remains:
When I load resources from the server (for example a GET request on http://localhost:8080/cars), the first time the collection of (in this case) cars is succesfully returned.
When I issue the same request for the second time, I always get the same result as the first time - even when the resources have changed in the meantime. When looking at my server, the second time there is no request issued at all.
I presume there's a caching mechanism implemented in RestSharp, but I see no way to invalidate the cache results.
Are there any ways to manually invalidate the RestSharp for Windows Phone cache results? (Or ways to force the library to get the results from the server)
You can control caching of resources by setting headers on the response your server sends back. If you do not want the resource to be cached then set the cache-control header to no-cache.
It is the server's job to specify how long a resource is good for, the client should do its best to respect that information.
If you really, really want to delete entries in the cache you need to go via the WinINet API
As a quick hack to avoid caching you can append a unique value to the end of the query string. The current DateTime (including seconds and milliseconds if necessary) or a GUID are suitable.
eg.
var uri = "http://example.com/myrequest?rand=" + DateTime.Now().ToString();
The Problem
There's an item (foo.js) that rarely changes. I'd like this item to be stored in the browser's cache (using Expires header). However, when it does change, I'd like the browser to update to the newest version.
The Attempt
Foo.js is returned with a far future Expires header. It's cached on the browser and requires no round trip query to the server. Just the way I like it. Now, when it changes....
Let's assume I know that the user's version of foo.js is outdated. How can I force a fresh copy of it to be obtained? I use xhr to perform a POST to foo.js. This should, in theory, force the browser to get a newer version of foo.js.
Unfortunately, this only seems to work in Firefox. Other browsers will use their cached version of the copy, even if other POST paramters are set.
WTF
First off, is there a way to do what I'm trying to do?
Second, why is there no sensible key/value type of cache that browser's have? Why can I not simply not include in headers: "Cache: some_key, some_expiration_time" and also specify "Clear-Cache: key1, key2, key3" (the keys must be domain specific, of course). Instead, we're stuck with either expensive round-trips that ask "is content new?", or the ridiculous "guess how long it'll be before you modify something" Expires header.
Thanks
Any comments on this matter are greatly appreciated.
Edits
I realize that adding a version number to the file would solve this. However, in my case it is not possible -- the call to "foo.js" is hardcoded into a bookmarklet.
You can just add a querystring to the end of the file, the server can ignore it, but the browser can't, it must treat it as a new request:
http://www.site.com/foo.js?v=1.12345
Many people use this approach, SO uses a hash of some sort, I use the build number (so users get a new version each build). If either of these is an option, you get the benefit of long duration cache headers, but still force a fetch of a new copy when needed.
Why set your cache expiration so far in the future? If you set it to one day for instance, the only overhead that you will incur (once a day) is the browser revalidating that it is the same file. If you still have not changed it, then you will not re-download the file, the server will respond with a not-modified response.
All caches have a set of rules that
they use to determine when to serve a
representation from the cache, if it’s
available. Some of these rules are set
in the protocols (HTTP 1.0 and 1.1),
and some are set by the administrator
of the cache (either the user of the
browser cache, or the proxy
administrator).
Generally speaking, these are the most
common rules that are followed (don’t
worry if you don’t understand the
details, it will be explained below):
If the response’s headers tell the cache not to keep it, it won’t.
If the request is authenticated or secure (i.e., HTTPS), it won’t be
cached.
A cached representation is considered fresh (that is, able to be
sent to a client without checking with
the origin server) if:
* It has an expiry time or other age-controlling header set, and
is still within the fresh period, or
* If the cache has seen the representation recently, and it was
modified relatively long ago.
Fresh representations are served directly from the cache, without
checking with the origin server.
If an representation is stale, the origin server will be asked to
validate it, or tell the cache whether
the copy that it has is still good.
Under certain circumstances — for example, when it’s disconnected
from a network — a cache can serve
stale responses without checking with
the origin server.
If no validator (an ETag or
Last-Modified header) is present on a
response, and it doesn't have any
explicit freshness information, it
will usually — but not always — be
considered uncacheable.
Together, freshness and validation are
the most important ways that a cache
works with content. A fresh
representation will be available
instantly from the cache, while a
validated representation will avoid
sending the entire representation over
again if it hasn’t changed.
http://www.mnot.net/cache_docs/#BROWSER
There is an excellent suggestion made in this thread: How can I make the browser see CSS and Javascript changes?
See the accepted answer by user, "grom".
The idea is to use the "modified" time stamp from the server to note when the file has been modified, and adding a version parameter to the end of the URL, making your CSS and JS files have URLs like this: my.js?version=12345678
This makes the browser think it is a new file, and so it does not refer to the cached version.
I am using a similar method in my app. It works pretty well. Of course, this would assume you are using something like PHP to process your HTML.
Here is another link with a more simple implementation for WordPress: http://markjaquith.wordpress.com/2009/05/04/force-css-changes-to-go-live-immediately/
With these constraints I guess your only option is to use window.location.reload(true) and force the browser to fresh all the cached items.. it's not pretty
You can invalidate cache on a specific url, using Cache-Control HTML header.
On your desired URL you can run (with xhr/ajax for instance) a request with following headers :
headers: {
'Cache-Control': 'no-cache, no-store, must-revalidate, max-age=0',
Pragma: 'no-cache',
Expires: '0',
}
Your cache will be invalidated, and next GET requests will return a brand new result.
I'm doing a little bit of ajax where I get a static html file that is actually changed on the disk from time to time. Of course IE has a problem where it wants to help out by caching the file which I don't want. I know how to fix this when grabbing a dynamic file: you just change the header in the dynamic file. But how do I do this for the static html file? Note that I am using apache.
Thanks
At Apache level you can setup the expiry date of the document using the mod_expires module.
From the documentation:
This module controls the setting of the Expires HTTP header and the max-age directive of the Cache-Control HTTP header in server responses. The expiration date can set to be relative to either the time the source file was last modified, or to the time of the client access.
These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.
More details at http://httpd.apache.org/docs/2.0/mod/mod_expires.html
If you can use mod_expires as Marcel suggested, you can always append a random request parameter.
For example, instead of requesting static_file.html you can request static_file.html?_=1231231231 and change that request parameter every time.
jQuery has a really simple way of doing this:
$.ajax({cache: false, url: static_file.html});